Optical sensors and specifically time-of-flight optical sensors for depth imaging suffer from a comparably high (i.e. poor) signal-to-noise ratio for electrical signals representing the time-of-flight which is the time needed for an electromagnetic signal such as e.g. light to travel from an active illumination source to an object and then back, or further on, to the optical sensor. The signal may be formed by amplitude modulation of the illumination source and the image relation in the optical sensor. Depending on the phase relation to the illumination source, only a fraction of the photo-generated charge carriers is directed towards a charge integration node which is read out after a certain integration time. As this charge is small, it is difficult to obtain a large signal voltage with respect to the noise source from the electronic read-out circuit.
Thus, the current design of time-of-flight sensors reveal essential limitations in the signal quality and, therefore, the precision of the time-of-flight measurement.